1. Field of the Invention
The present invention relates to a substrate holding apparatus for holding a substrate to be polished and pressing the substrate against a polishing surface, and more particularly to a substrate holding apparatus for holding a substrate such as a semiconductor wafer in a polishing apparatus for polishing the substrate. The present invention also relates to a dressing apparatus for dressing a polishing surface by bringing a dressing member in sliding contact with the polishing surface, and more particularly to a dressing apparatus in the above polishing apparatus.
2. Description of the Related Art
In a manufacturing process of a semiconductor device, a thin film is formed on a semiconductor device, and then micromachining processes, such as patterning or forming holes, are performed. Thereafter, these processes are repeated to form thin films on the semiconductor device. Recently, semiconductor devices have become more integrated, and structure of semiconductor elements has become more complicated. In addition, a number of layers in multilayer interconnections used for a logical system has been increased. Therefore, irregularities on a surface of the semiconductor device are increased, so that a step height on the surface of the semiconductor device becomes larger.
When irregularities on the surface of the semiconductor device are increased, the following problems arise. Thickness of a film formed in a portion having a step is relatively small. An open circuit is caused by disconnection of interconnections, or a short circuit is caused by insufficient insulation between the layers. As a result, good products cannot be obtained, and yield is reduced. Further, even if a semiconductor device initially works normally, reliability of the semiconductor device is lowered after long-term use. At a time of exposure in a lithography process, if an irradiation surface has irregularities, then a lens unit in an exposure system is locally unfocused. Therefore, if irregularities on the surface of the semiconductor device are increased, then it is difficult to form a fine pattern on the semiconductor device.
Thus, in a manufacturing process of a semiconductor device, it is increasingly important to planarize a surface of the semiconductor device. The most important one of planarizing technologies is chemical mechanical polishing (CMP). In chemical mechanical polishing using a polishing apparatus, while a polishing liquid containing abrasive particles such as silica (SiO2) therein is supplied onto a polishing surface such as a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing surface, so that the substrate is polished.
This type of polishing apparatus comprises a polishing table having a polishing surface constituted by a polishing pad (or a fixed abrasive), and a substrate holding apparatus, such as a top ring or a carrier head, for holding a semiconductor wafer. When a semiconductor wafer is polished with this type of polishing apparatus, the semiconductor wafer is held by the substrate holding apparatus and pressed against the polishing table under a predetermined pressure. At this time, the polishing table and the substrate holding apparatus are moved relatively to each other to bring the semiconductor wafer into sliding contact with the polishing surface, so that a surface of the semiconductor wafer is polished to a flat mirror finish.
When the semiconductor wafer is polished with such a polishing apparatus, a polishing liquid or ground-off particles of semiconductor material are attached to the polishing surface (polishing pad), resulting in a change in properties of the polishing pad and deterioration in polishing performance. Therefore, if an identical polishing pad is repeatedly used for polishing semiconductor wafers, problems such as lowered polishing rate and uneven polishing are caused. Therefore, a dressing apparatus (dresser) is provided adjacent to the polishing apparatus to regenerate the surface of the polishing pad which has deteriorated due to polishing. In a dressing process, while a dressing member attached to a lower surface of the dresser is pressed against the polishing pad (polishing surface) on the polishing table, the polishing table and the dresser are independently rotated to remove the polishing liquid and the ground-off particles of the semiconductor material which are attached to the polishing surface, and to flatten and dress the polishing surface. The dressing member generally comprises a dressing surface on which diamond particles are electrodeposited, and the dressing surface is brought into contact with the polishing surface. This dressing process is also referred to as a conditioning process.
In the above polishing apparatus, if relative pressure between a semiconductor wafer which is being polished and the polishing surface of the polishing pad is not uniform over an entire surface of the semiconductor wafer, then the semiconductor wafer may be insufficiently polished or may be excessively polished depending on pressure applied to the semiconductor wafer. Therefore, it has been attempted to define a hermetically sealed chamber within a substrate holding apparatus with an elastic membrane, and supply a fluid under a predetermined pressure to the hermetically sealed chamber for thereby controlling pressure imposed on a semiconductor wafer by the substrate holding apparatus.
In the process of dressing the polishing surface on the polishing table with the dresser, since the polishing surface is scraped by a dressing action, if a dressing load under which the dressing member is pressed against the polishing surface is large, then service life of the polishing pad (or fixed abrasive) is shortened, and a cost of the polishing apparatus is increased. Therefore, it has also been attempted to define a hermetically sealed chamber within the dresser with an elastic membrane, and supply a fluid under a predetermined pressure to the hermetically sealed chamber for thereby controlling a dressing load.
However, in a case of the substrate holding apparatus for polishing a semiconductor wafer while controlling pressure applied to the semiconductor wafer, if a leakage occurs from the hermetically sealed chamber due to a crack or a break in the elastic membrane, then pressure in the hermetically sealed chamber may not be kept at a preset level, and the semiconductor wafer being polished may be broken.
Similarly, in a case of the dresser for dressing the polishing surface while controlling the dressing load, if a leakage occurs from the hermetically sealed chamber and pressure in the hermetically sealed chamber is not kept at a preset level, then the polishing surface may be damaged and the dresser itself may be broken due to an uneven dressing load.